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Optimal Timing of Pavement Preventive Maintenance Treatment Applications (2004)

Chapter: Chapter 2 - Background and Literature Search

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Suggested Citation:"Chapter 2 - Background and Literature Search." National Academies of Sciences, Engineering, and Medicine. 2004. Optimal Timing of Pavement Preventive Maintenance Treatment Applications. Washington, DC: The National Academies Press. doi: 10.17226/13772.
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Suggested Citation:"Chapter 2 - Background and Literature Search." National Academies of Sciences, Engineering, and Medicine. 2004. Optimal Timing of Pavement Preventive Maintenance Treatment Applications. Washington, DC: The National Academies Press. doi: 10.17226/13772.
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Suggested Citation:"Chapter 2 - Background and Literature Search." National Academies of Sciences, Engineering, and Medicine. 2004. Optimal Timing of Pavement Preventive Maintenance Treatment Applications. Washington, DC: The National Academies Press. doi: 10.17226/13772.
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Suggested Citation:"Chapter 2 - Background and Literature Search." National Academies of Sciences, Engineering, and Medicine. 2004. Optimal Timing of Pavement Preventive Maintenance Treatment Applications. Washington, DC: The National Academies Press. doi: 10.17226/13772.
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Suggested Citation:"Chapter 2 - Background and Literature Search." National Academies of Sciences, Engineering, and Medicine. 2004. Optimal Timing of Pavement Preventive Maintenance Treatment Applications. Washington, DC: The National Academies Press. doi: 10.17226/13772.
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Suggested Citation:"Chapter 2 - Background and Literature Search." National Academies of Sciences, Engineering, and Medicine. 2004. Optimal Timing of Pavement Preventive Maintenance Treatment Applications. Washington, DC: The National Academies Press. doi: 10.17226/13772.
×
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Suggested Citation:"Chapter 2 - Background and Literature Search." National Academies of Sciences, Engineering, and Medicine. 2004. Optimal Timing of Pavement Preventive Maintenance Treatment Applications. Washington, DC: The National Academies Press. doi: 10.17226/13772.
×
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Suggested Citation:"Chapter 2 - Background and Literature Search." National Academies of Sciences, Engineering, and Medicine. 2004. Optimal Timing of Pavement Preventive Maintenance Treatment Applications. Washington, DC: The National Academies Press. doi: 10.17226/13772.
×
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Suggested Citation:"Chapter 2 - Background and Literature Search." National Academies of Sciences, Engineering, and Medicine. 2004. Optimal Timing of Pavement Preventive Maintenance Treatment Applications. Washington, DC: The National Academies Press. doi: 10.17226/13772.
×
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Suggested Citation:"Chapter 2 - Background and Literature Search." National Academies of Sciences, Engineering, and Medicine. 2004. Optimal Timing of Pavement Preventive Maintenance Treatment Applications. Washington, DC: The National Academies Press. doi: 10.17226/13772.
×
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Suggested Citation:"Chapter 2 - Background and Literature Search." National Academies of Sciences, Engineering, and Medicine. 2004. Optimal Timing of Pavement Preventive Maintenance Treatment Applications. Washington, DC: The National Academies Press. doi: 10.17226/13772.
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7CHAPTER 2 BACKGROUND AND LITERATURE SEARCH INTRODUCTION The first step in developing a methodology for determining the optimal timing of preventive maintenance was to review and assess previously completed work on this topic. As part of that effort, a literature search was performed and appro- priate types of treatments used for preventive maintenance were identified. This chapter highlights the findings from the literature search and identifies important characteristics of preventive maintenance treatments. The literature search focused on the topics relevant to pre- ventive maintenance application timing, specifically the fol- lowing topics: • Concepts and implementation • Case studies • Measurement of benefit • Maintenance costs • Maintenance treatment selection and performance • Treatment application timing • Optimization methods From approximately 200 records that were reviewed, only a few of the published reports specifically discussed treatment timing issues, and none provided any indication of rigorous research into the development of guidelines for the optimal timing of preventive maintenance. Nonetheless, a good deal of information was available for the other areas targeted in the literature search. Some of the findings regarding the con- cepts, implementation, and state agency experience (case stud- ies) of preventive maintenance are highlighted in Chapter 1. A more detailed discussion of treatment selection, usage, and performance is presented later in this chapter. Benefit- and cost-related information is included in the discussion of the analysis approach described in Chapter 3. Finally, the pub- lished work on optimization approaches is summarized and presented in Appendix B. Overview of Preventive Maintenance Experience with preventive maintenance in the United States differs substantially among highways agencies. For example, Arizona (8) and Iowa (9) have constructed test sec- tions to evaluate the performance of certain preventive maintenance treatments; Michigan, New York, and Califor- nia have well-established preventive maintenance programs which are documented in comprehensive manuals. In light of this broad range of experience, it is noteworthy to review the status of pavement preservation in the United States. In 1999, transportation agencies in all 50 states, the District of Columbia, Puerto Rico, and six Canadian Provinces were sur- veyed about their preventive maintenance programs and prac- tices; 41 agencies responded (10). All 41 respondents reported using preventive treatments. Eighty-five percent (36) of the respondents reported having established pavement preventive maintenance programs, and two respondents were in the pro- cess of establishing a program. Seventeen of the respondents reported having a program in place for more than 10 years, and one agency reported practicing preventive maintenance for the past 75 years. Regarding the condition of pavement when applying pre- ventive maintenance treatments, 25 respondents said that pavements were in good condition, 22 said that they were in poor condition, and 1 respondent said they were in very poor condition (note that respondents identified all conditions in which maintenance treatment is applied). Some respondents noted that “preventative maintenance techniques are some- times applied to poor roads when reconstruction budgets are limited,” and “all pavements are treated, based on the assump- tion that even poor pavements will receive some benefit, how- ever small.” The confusion about preventive maintenance stems in part from the fact that the condition in which a treatment is used— not the characteristics of the treatment—is what defines the treatment as “preventive.” A treatment that is used to extend pavement life or improve functional performance may also be used to hold the pavement together until a rehabilitation or reconstruction project can be scheduled. Therefore, when using a treatment as a preventive application, the following three items must be considered: • Existing distresses to be treated, or anticipated distresses to be prevented or slowed; • Most appropriate treatments for existing conditions; and • Timing the treatment for best results (i.e., maximizing performance while minimizing overall costs).

Thus, a thin overlay should not be considered a preventive maintenance treatment when it is applied to badly alligator- cracked pavement, neither should a slurry seal when it is placed on a cracked and oxidized surface. Selecting the appro- priate treatment together with determining the appropriate tim- ing of its placement constitutes a preventive maintenance strat- egy. These elements of preventive maintenance are captured in the following definition (1): . . . the planned strategy of cost effective treatments to an existing roadway system and its appurtenances that pre- serves the system, retards future deterioration, and main- tains or improves the functional condition of the system [without increasing structural capacity]. Many factors should be considered when selecting the most appropriate preventive maintenance treatment for a given pavement. Some of those factors relate to the limitations of the treatments; important attributes or characteristics of some of the common preventive maintenance treatments are described later in this chapter. Constructibility and customer satisfac- tion are other factors to consider. Constructibility pertains to the availability of skilled contractors and suitable materials, environmental constraints, and other factors such as traffic control constraints and available lane closures that affect the placement of the treatments. Customer satisfaction pertains to traffic disruption, noise impacts, surface friction, and ride quality; it is becoming increasingly important for many agen- cies. While all these issues are important, this project focuses on performance attributes. These attributes include the treat- ment’s expected life, the effect of the existing pavement con- dition on performance of the treatment, the effect of the treat- ment on the pavement condition, the effect of the climate on treatment performance, and the treatment cost. Pavement Deterioration and Treatment Timing Deterioration of a well designed and constructed pave- ment occurs as a result of the effects of the environment, the 8 traffic loads, and the interaction between the two. However, initial deterioration results almost solely from environmental effects. It is a fundamental tenet of treatment performance that the same treatment performs differently when applied at differ- ent times in the life of the pavement (or on pavements in varying condition). For example, placing a thin bituminous surfacing (such as a chip seal) on top of a 2-month old pave- ment may not increase the pavement’s life because the pave- ment may show structural deterioration once the surfacing wears off. Similarly, placing the same treatment near the end of the pavement’s life (i.e., when the surface is aged and worn and the pavement is exhibiting signs of structural dete- rioration) will have a minimal effect on pavement perfor- mance because the condition of the underlying pavement will control performance. Therefore, for a given pavement, there is an optimal age or condition (or a range of age or condition) where the benefit/cost (B/C) ratio associated with a chosen treatment is maximized; this is defined as the optimal timing for the treatment. PREVENTIVE MAINTENANCE TREATMENTS FOR BITUMINOUS- AND CONCRETE-SURFACED PAVEMENTS Different approaches are used to identify which pavement treatments are considered “preventive.” For example, the Michigan DOT (MDOT) preventive maintenance program lists the 20 treatments shown in Table 1 (11). In Caltrans’ Capital Preventive Maintenance (CAPM) program, grinding and removal and replacement of failed slabs are described for concrete-surfaced pavements, and thin overlays and “pre- mium seal coats” (microsurfacing, polymer- and rubber- modified chip seals, modified binder open-graded hot-mix asphalt (HMA) blankets, and thin, hot-applied, gap-graded applications) are described for bituminous-surfaced pavements (12). In an FHWA course on pavement preservation, at least 11 bituminous-surfaced pavement treatments and 8 concrete- surfaced pavement treatments are described (13). Concrete-Surfaced Pavements Bituminous-Surfaced Pavements Full depth concrete pavement repair Joint resealing Crack sealing Joint and surface spall repair Dowel bar retrofit Diamond grinding Underdrain outlet repair and cleaning Concrete pavement restoration Bituminous shoulder ribbons Bituminous overlay Surface milling and bituminous overlay Ultrathin bituminous overlay Crack treatment Overband crack filling Microsurfacing Chip seals Bituminous shoulder ribbons Shoulder seals Paver placed surface seals Hot in-place bituminous recycling TABLE 1 Treatments included in MDOT’s 1999 and 2000 Capital Preventive Maintenance program (11)

Industry and agencies are constantly identifying new approaches to treating pavements, while discarding others that have been shown not to work for them. Key components in an agency’s decision process for selecting a specific treat- ment are (1) determining timing and (2) understanding impor- tant attributes of the treatment. In a methodical approach to identifying appropriate treatments, the performance charac- teristics or attributes of the treatments must be considered because these alone determine if a treatment can serve its intended purpose. Treatment Attributes Treatments that are suitable for use by a given agency can be identified by considering the following factors or treat- ment attributes: • Purpose of the treatment • Applicability – Traffic – Environment – Pavement condition • Contraindications • Construction considerations • Expected performance and cost • Customer satisfaction Purpose of the Treatment The purpose of the treatment involves identifying pave- ment conditions that the treatment is meant to prevent or cor- rect. For example, sealing cracks prevents moisture (and debris) from infiltrating the pavement structure. Some treat- ments may serve several purposes; a slurry seal can protect an HMA surface from environmental effects, improve sur- face friction, or seal minor cracks in the pavement surface. Any treatment considered for a preventive maintenance pro- gram should address one or more specific purposes so that the conditions of its use are clear. Because some of the preven- tive maintenance treatments are applied to pavement with lit- tle or no signs of deterioration, the purpose is not always to correct distress. Applicability The applicability or appropriateness of a treatment is deter- mined by the overall condition of the pavement, traffic, and environment for which the treatment is suited. For example, some treatments require application at fairly warm tempera- tures to ensure good long-term performance, and their use is not recommended if a prolonged period of warm weather can- 9 not be forecast. Other factors that may influence the treat- ment selection process include the extent of snow plowing, the use of studded tires or chains, and the lane closure time available to complete the work. Traffic is another important consideration as treatments perform differently under traffic loads. Many agencies differ- entiate appropriate treatments based on daily traffic counts or loads. This information can serve several purposes. For some treatments, the higher volume of traffic contributes to a like- lihood of vehicle damage. Other treatments might be chosen because high-traffic volumes are anticipated and the treat- ment may reduce the likelihood of pavement deterioration. The condition of the pavement cannot be ignored in deter- mining appropriate treatments. While the concept of preven- tive maintenance implies that the pavement exhibits minimal distresses, the reality is that many treatments will be applied to pavements with some distress. It is important to know what distresses are present and how the different treatments will perform in relation to those distresses. Contraindications Conditions under which a specific treatment simply will not work or should not be used are considered contraindications for this treatment. For example, the need for a complete clo- sure of the pavement, the requirement for cure time after appli- cation and before loads can be applied, the potential damage from early application of heavy loads, and the possible failure because of the presence of moisture during construction might all be considered contraindications to the use of certain treat- ments. While improvements in the technology of many pre- ventive maintenance treatments help extend the conditions under which they can be used, familiarity with their limitations also helps to obtain the best possible performance. Construction Considerations Constructibility issues that need to be considered include the complexity of the construction of the treatment, the need for specialized or well-calibrated equipment, the local avail- ability of qualified contractors, and the need for specialized materials. If a treatment’s success relies on factors that are beyond the control of the agency, its application may be viewed as less feasible than a treatment that can be placed by most contractors using locally available materials. Expected Performance and Cost Another set of considerations relates to the performance and cost associated with a given treatment. An agency should be aware of both the expected performance of the treatment and

its cost to determine if that combination of performance and cost is acceptable. This information will also help compare dif- ferent alternatives for reaching similar objectives. If adequate information about treatment performance is not readily avail- able, agencies are strongly encouraged to generate preventive maintenance treatment performance data based on their own experience. In the interim, data required to perform certain analysis may be obtained from other sources, such as “expert” opinion or other agencies with comparable conditions. Customer Satisfaction There is a growing emphasis in highway agencies to pur- sue actions that improve customer satisfaction. Some of the attributes of interest to the traveling public include noise, roughness, absence from splash and spray, and traffic dis- ruptions from road repairs. Different treatments affect these attributes in different ways, and an agency interested in improv- ing customer satisfaction will consider these factors in the treatment selection process. Characteristics of Selected Treatments A list of pavement treatments that meet the definition of “preventive” maintenance is shown in Table 2; characteris- tics of treatments for bituminous- and concrete-surfaced pavements are presented in Tables 3 through 14 and mainte- nance of drainage features are shown in Table 15. This infor- mation includes estimates of the expected life and typical 10 cost of each treatment. Because the expected life estimates reported in these tables are based on the use of the treatment in both a preventive and reactive manner, there is a broad range for some of the reported lives. The costs also cover a wide range of applications and regional variations; users are encouraged to identify local, and more recent values for use in the analysis. Overview of Treatments for Bituminous-Surfaced Pavements With the exception of crack filling and crack sealing, treatments described in this section consist of a thin, uniform TABLE 2 Typical pavement preventive maintenance treatments 1. Bituminous-Surfaced Pavements Crack Filling/Crack Sealing Fog Seals Slurry Seals Scrub Seals Microsurfacing Chip Seals Thin Overlay Ultrathin Friction Courses 2. Concrete-Surfaced Pavements Joint/Crack Sealing Diamond Grinding Undersealing Load Transfer Restoration 3. Maintenance of Drainage Features EVALUATION FACTORS CRACK FILLING AND CRACK SEALING Climate Traffic Conditions Addressed Contraindications Description: These treatments are intended primarily to prevent the intrusion of moisture through existing cracks. Crack sealing refers to a sealant operation that addresses “working” cracks, i.e., those that open and close with changes in temperature. It typically implies high quality materials and good preparation. Crack filling is for cracks that undergo little movement. Sealants used are typically thermo-plastic (bituminous) materials that soften upon heating and harden upon cooling. Treatment can perform well in all climatic conditions. However, sealants perform best in dryer and warmer environments that do not undergo large daily temperature changes. Performance is not significantly affected by varying ADT or truck levels. Functional/Other ■ ■ ■ Longitudinal cracking Minor block cracking Transverse cracking Structural Adds no structural benefit, but does reduce moisture infiltration through cracks. Only practical if the extent of cracking is minimal and if there is little to no structural cracking. ■ Structural failure (i.e., extensive fatigue cracking or high severity rutting) ■ Extensive pavement deterioration, little remaining life Site Restrictions None. Construction Considerations Placement should be done during cool, dry weather conditions. Proper crack cleaning is essential to a good bond and maximum performance. Some agencies also use hot compressed air lance prior to sealing. Expected Life 2 to 6 years. Typical Costs $1.00 to $5.00 per linear m ($0.30 to $1.50 per linear ft) for crack sealing, including routing; $1.00 per linear m ($0.30 per linear ft) for crack filling. Costs are slightly higher for small jobs. TABLE 3 Characteristics of crack filling and crack sealing

11 EVALUATION FACTORS FOG SEALS Climate Traffic Conditions Addressed Contraindications Fog seals are very light applications of a diluted asphalt emulsion placed directly on the pavement surface with no aggregate. Typical application rates range from 0.23 to 0.45 liters per m2 (0.05 to 0.10 gal per yd2). Treatment performs well in all climatic conditions. Actual performance will vary according to factors that affect weathering and raveling of bituminous surfaces. Increased ADT or truck levels can increase surface wear, particularly in states that permit studded tires. Functional/Other ■ ■ ■ ■ Longitudinal, transverse, and block cracking (M) Raveling/weathering (loose material must be removed) Asphalt aging, oxidation and hardening Moisture infiltration Structural Adds no structural benefit, but can help reduce moisture infiltration through fatigue cracks (if their severity is low) ■ ■ ■ ■ Structural failure (such as significant fatigue cracking) Flushing/bleeding (M) Friction loss (M-H) Thermal cracking (H) Site Restrictions Not appropriate for surfaces with poor skid resistance, as it will lower the skid resistance even more. Construction Considerations Typically, a slow-setting emulsion is used which requires time to “break,” the pavement is sometimes closed for 2 hours for curing before being re-opened to traffic. Expected Life 1 to 2 years when placed in a preventive maintenance mode. Typical Costs $0.36 to $0.54 per m2 ($0.30 to $0.45 per yd2) of pavement surface area. Note: L, M, and H define level of distress (L for low, M for medium, and H for high). Description: Fog seals are placed primarily to seal the pavement, inhibit raveling, enrich the hardened/ oxidized asphalt, and provide some pavement edge-shoulder delineation. TABLE 4 Characteristics of fog seals EVALUATION FACTORS SLURRY SEALS Climate Traffic Conditions Addressed Contraindications Description: A mixture of well-graded aggregate (fine sand and mineral filler) and asphalt emulsion that is spread over the entire pavement surface with either a squeegee or spreader box attached to the back of a truck. It is effective in sealing low-severity surface cracks, waterproofing the pavement surface, and improving skid resistance at speeds below 64 km/h (30 mph). Thickness is generally less than 10 mm (0.4 in.). Treatment performs effectively in all climatic conditions. However, best performance occurs in warm climates with low daily temperature changes. Performance in terms of surface wear is affected by increasing ADT and truck traffic levels. Slurry mix properties (i.e., aggregate quality, gradation and emulsion content) can be modified to accommodate the higher traffic volumes. Functional/Other ■ Transverse, longitudinal and block cracking (L) ■ Raveling/weathering (loose material must be removed) ■ Asphalt aging, oxidation and hardening ■ Friction loss ■ Moisture infiltration Structural Adds no structural capacity; however, can temporarily seal cracks (if severity is low) or serve as a rut-filler (if the ruts are not severe and are stable) ■ Structural failure (such as significant fatigue cracking and deep rutting) ■ Thermal cracking (H) ■ Can accelerate the development of stripping in susceptible HMA pavements Site Restrictions Pavement is often closed for several hours to allow the emulsion to cure. Construction Considerations Surface must be clean. Aggregates must be clean, angular, durable, well-graded, and uniform (prefer 100% crushed). Avoid placement in hot weather (potential flushing problems) and premature opening to traffic. Do not place when freezing temperatures are expected. Expected Life 3 to 5 years when placed in a preventive maintenance mode. Typical Costs $0.84 to $1.14 per m2 ($0.70 to $1.00 per yd2). Additional Information Three slurry types with different aggregate gradations and application rates are used: Type I for lower traffic volume (3.3 to 5.4 kg/m2 [6.1 to 10.0 lb/yd2]) Type II for heavy traffic (5.4 to 8.1 kg/m2 [10.0 to 15.0 lb/yd2]) and Type III for irregular surfaced pavements (8.1 kg/m2 [15.0 lb/yd2]). Note: L, M, and H define level of distress (L for low, M for medium, and H for high). TABLE 5 Characteristics of slurry seals

treatment applied to the pavement surface. If unsealed, the surface bituminous material loses volatiles as it is exposed to environmental forces, dries out, becomes brittle, begins to lose aggregate (raveling), and cracks. Thin surfacings seal the pavement surface slowing the aging process of the sur- face materials. These surfacings range from a fog seal (an asphalt emulsion without any aggregate) to a thin HMA over- 12 lay; they cover the pavement surface without a structural con- tribution. Corrective measures, such as crack filling or crack sealing, can also improve long-term performance by keeping the pavement structure free from moisture infiltration, which otherwise could contribute to weakening the pavement. Addi- tional characteristics of each of these treatments are summa- rized in Tables 3 through 11. EVALUATION FACTORS SCRUB SEALS Climate Traffic Conditions Addressed Contraindications Description: A four-step process intended to rejuvenate the asphalt surface and to fill voids and surface cracks: (1) application of a layer of polymer-modified asphalt emulsion that is broomed into the voids and cracks of the pavement, (2) application of sand or small-sized aggregate, (3) a second application of polymer- modified asphalt (by brooming), and (4) rolling with a pneumatic- tired roller. Can be effective in all climates, but works best in hot, arid climates. Good performance has been observed on lower- volume roads (less than 7,500 ADT) Functional/Other ■ Transverse, longitudinal and block cracking (L) ■ Raveling/weathering (loose material must be removed) ■ Moisture infiltration Structural Adds no structural capacity; however, can help seal cracks (if severity is low) ■ Structural failure (such as significant fatigue cracking) ■ Thermal cracking (H) Site Restrictions Do not apply on tight surfaces as this may reduce skid resistance of the pavement. Construction Considerations Surface must be clean; special equipment is required for brushing. Expected Life 1 to 3 years when placed in a preventive maintenance mode. Typical Costs $0.90 to $1.49 per m2 ($0.75 to $1.25 per yd2). Additional Information Generally easy to apply and relatively inexpensive. Note: L, M, and H define level of distress (L for low, M for medium, and H for high). TABLE 6 Characteristics of scrub seals EVALUATION FACTORS MICROSURFACING Climate Traffic Conditions Addressed Contraindications Description: Microsurfacing consists of a mixture of polymer-modified emulsified asphalt, mineral aggregate, mineral filler, water, and additives applied in a process similar to slurry seals. Used primarily to inhibit raveling and oxidation of the pavement surface. Also effective at improving surface friction, and filling minor irregularities and wheel ruts (up to 40 mm [1.6 in.] deep) in one pass. Effective in all climate conditions. However, best performance occurs in warm climates with low daily temperature changes. May not set up quickly if applied in cool climates. Very successful on both low- and high- volume roadways. Functional/Other ■ Longitudinal and transverse cracking (L) ■ Raveling/weathering (loose material must be removed) ■ Bleeding (L-M) ■ Roughness (L) ■ Friction loss ■ Moisture infiltration Structural Adds limited structural capacity. Temporarily seals fatigue cracks (if severity is low) and can serve as a rut-filler (if the existing ruts are stable) ■ Structural failure (i.e., extensive fatigue cracking) ■ Extensive pavement deterioration, little remaining life ■ Thermal cracks (H) ■ Can accelerate the development of stripping in susceptible HMA pavements Site Restrictions None. Construction Considerations Avoid placement in hot weather if there is potential for flushing problems. Placement in cool weather can lead to early raveling, not to be placed when freezing temperatures are expected. Expected Life 4 to 7 years when placed in a preventive maintenance mode. Typical Costs $1.05 to $2.00 per m2 ($0.90 to $1.70 per yd2). Additional Information Typical mix proportions: 82 to 90% aggregate, 1.5 to 3.0% mineral filler, and 5.5 to 9.5% residual asphalt. Note: L, M, and H define level of distress (L for low, M for medium, and H for high). TABLE 7 Characteristics of microsurfacing

13 EVALUATION FACTORS CHIP SEALS Climate Traffic Conditions Addressed Contraindications Description: Asphalt (commonly an emulsion) is applied directly to the pavement surface (1.59 to 2.27 L/m2 [0.35 to 0.50 gal/yd2]) followed by the application of aggregate chips (8 to 27 kg/m2 [15 to 50 lb/yd2]), which are then immediately rolled to imbed chips (50 to 70 percent). Application rates depend upon aggregate gradation and maximum size. Treatment seals pavement surface and improves friction. Treatment performs well in all climatic conditions. With proper design and placement, chip seals can perform well on high-volume roads. However, use is primarily limited to lower-speed, lower- volume roads because of the propensity for loose chips to crack windshields. Functional/Other ■ Longitudinal, transverse and block cracking ■ Raveling/weathering (loose surface material must be removed) ■ Friction loss ■ Roughness (L) ■ Bleeding (L) ■ Moisture infiltration Structural Adds almost no structural capacity. However, effective at sealing fatigue cracks (M) in comparison with other treatments. ■ Structural failure (i.e., extensive fatigue cracking and/or deep rutting) ■ Thermal cracking (H) ■ Extensive pavement deterioration, little or no remaining life ■ Can accelerate the development of stripping in susceptible HMA pavements Site Restrictions High-speed, high-volume roadways are often avoided, although a number of approaches are being used to extend the applicability of these treatments. Construction Considerations Surface must be clean. Treatment should be placed during warm weather with chip spreader immediately behind asphalt distributor and rollers close behind the spreader. Approximately 2 hours required before roadway may be re-opened to normal speed traffic. Brushing is usually required to remove loose chips. Expected Life 4 to 7 years when placed in a preventive maintenance mode. Typical Costs $0.90 to $1.08 per m2 ($0.75 to $0.90 per yd2) for a single application and $1.32 to $1.49 per m2 ($1.10 to $1.25 per yd2) for a double application. Additional Information A second chip seal may be placed to achieve improve performance. Total thickness may approach 25 mm (1 in.). Note: L, M, and H define level of distress (L for low, M for medium, and H for high). TABLE 8 Characteristics of chip seals EVALUATION FACTORS THIN HOT-MIX ASPHALT OVERLAYS Climate Traffic Conditions Addressed Contraindications Description: Plant-mixed combinations of asphalt cement and aggregate applied to the pavement in thicknesses between about 19 and 38 mm (0.75 and 1.50 in.). Dense-graded, open-graded, and stone matrix mixes are used. Treatment performs well in all climatic conditions. Actual performance will vary according to factors that affect weathering and raveling of bituminous surfaces. Performance should not be affected by different ADT or percent trucks. Thin HMA overlays are not structural layers and as such should not be subjected to strain from loadings. Such layers may be subject to top- down cracking under certain combinations of loadings, environmental conditions, and pavement structures. Functional/Other ■ Longitudinal and transverse cracking (L) ■ Raveling/weathering (loose surface material must be removed) ■ Friction loss ■ Roughness ■ Bleeding (L) ■ Block cracking (L; may perform better with additional milling) Structural Rutting (assumes rutting has stopped; requires use of separate rut-fill application) ■ Structural failure (i.e., fatigue cracking) ■ Extensive pavement deterioration, little remaining life ■ Thermal cracking (H) Site Restrictions Edge-shoulder drop-off should be considered. Surface should be uniform to ensure uniform compaction. Construction Considerations Surface must be clean. A tack coat prior to overlay placement will help improve the bond to the existing surface. Thin HMA overlays dissipate heat rapidly and, therefore, depend upon minimum specified mix placement temperatures and timely compaction. Expected Life 7 to 10 years when placed in a preventive maintenance mode. Typical Costs $2.09 to $2.39 per m2 ($1.75 to $2.00 per yd2) for dense-graded mixes; $1.50 to $1.70 per m2 ($1.25 to $1.42 per yd2) for open-graded mixes. Additional Information While thin HMA overlays are considered a functional treatment, repetitive applications will impart some structural benefit to the pavement in the form of additional load-carrying capability. Note: L, M, and N define level of distress (L for low, M for medium, and H for high). TABLE 9 Characteristics of thin hot-mix asphalt overlays

14 EVALUATION FACTORS ULTRATHIN FRICTION COURSES Climate Traffic Conditions Addressed Contraindications Description: Relatively new treatment in the U.S. Consists of a gap-graded, polymer- modified 10 to 20 mm (0.4 to 0.8 in.) HMA layer placed on a tack coat formed by the application of a heavy, polymer-modified asphalt emulsion. Treatment effectively addresses minor surface distresses and increases surface friction. Treatment should perform well in all climatic conditions. Capable of withstanding high ADT volumes and truck traffic better than other thin treatments. Functional/Other ■ Longitudinal, transverse and block cracking (L). Higher severities can be addressed with cold milling. ■ Raveling/weathering (loose surface material must be removed) ■ Friction loss (H) ■ Roughness (L) ■ Bleeding (L) Structural Provides some increased capacity and retards fatigue cracking. Not suited for rutted pavements. ■ Structural failure (i.e., significant fatigue cracking and/or deep rutting) ■ Extensive pavement deterioration, little remaining life ■ Thermal cracking (H) Site Restrictions Ultrathin overlays should only be placed on structurally sound pavements. Localized structural problems should be repaired prior to overlay application. Construction Considerations Requires special paving equipment to place the mix and a license to apply it. Expected Life 7 to 10 years when placed in a preventive maintenance mode. Typical Costs $3.00 to $3.59 per m2 ($2.50 to $3.00 per yd2), or about 50 percent more than thin, dense-graded HMA overlay. Additional Information A proprietary treatment is known in the U.S. as “Novachip.” Note: L, M, and H define level of distress (L for low, M for medium, and H for high). TABLE 10 Characteristics of ultrathin friction courses EVALUATION FACTORS JOINT RESEALING AND CRACK SEALING Climate Traffic Conditions Addressed Contraindications Description: Resealing of transverse joints and sealing of cracks in PCC pavements is intended to minimize the infiltration of surface water into the underlying pavement structure and to prevent the intrusion of incompressibles into the joint. A range of materials including bituminous, silicone, and neoprene are used in designed configurations. Sealing of PCC pavement joints and cracks performs well in all climatic conditions. Sealant performance is affected by environmental conditions and the performance of sealed and unsealed pavement structures probably varies within environmental regions. ■ Performance is not affected by different ADT or percent trucks. ■ Silicone sealants that are not properly recessed are more likely to fail in the wheelpath. Functional/Other ■ Longitudinal and transverse cracking (L) ■ Unsealed or partially sealed joints. Structural No direct structural benefit, but may reduce rate of structural deterioration. Sealing may also be beneficial on a structurally failing pavement to prolong the time until rehabilitation. Crack sealing is not an effective method of repairing cracked slabs, but may be useful in preventing further deterioration. Different materials can be expected to perform for different durations. Material selection should be based on the expected time until next treatment. Site Restrictions Sealant reservoir should be clean and dry. Variable width reservoirs may cause a problem where backer rods are specified. Construction Considerations Sealant performance is dependent on many construction factors, including material type and placement geometry, and application in a clean and dry environment. Expected Life 7 to 8 years. Typical Costs $2.50 to $4.00 per linear m ($0.75 to $1.25 per linear ft) for hot-pour rubberized materials and from about $3.25 to $6.50 per linear m ($1.00 to $2.00 per linear ft) for silicone materials. Additional Information While the merits of joint sealing in new construction is currently being questioned, this debate has not extended to the merits of keeping existing pavements sealed. Note: L, M, and H define level of distress (L for low, M for medium, and H for high). TABLE 11 Characteristics of joint resealing and crack sealing

15 Overview of Treatments for Concrete-Surfaced Pavements The preventive maintenance treatments for concrete-surfaced pavements function in a different manner than those for bitu- minous-surfaced pavements. The identified treatments can be used to anticipate and mitigate more serious deterioration. Ben- efits of these treatments include reduced roughness, improved skid resistance, and protection against distresses accelerated by the presence of subsurface moisture (such as pumping, fault- ing, and corner breaks). Key characteristics of the concrete pavement treatments are summarized in Tables 11 through 14. EVALUATION FACTORS DIAMOND GRINDING Climate Traffic Conditions Addressed Contraindications Description: Diamond grinding is the removal of a thin layer of concrete (generally about 6.4 mm [0.25 in.]) from the surface of the pavement, using special equipment outfitted with a series of closely spaced diamond saw blades. The major applications for diamond grinding are to remove surface irregularities (most commonly joint faulting), to restore a smooth- riding surface, and to increase pavement surface friction (14). Diamond grinding performance is not affected by climate. However, if studded snow tires or chains are used, surface wear may require more frequent grinding to restore friction. Diamond grinding performance may be affected by traffic. Grinding may be used to remove faulting, which can reoccur due to the continued application of truck traffic. If grinding is used to restore friction loss caused by polishing of the pavement surface due to vehicle traffic, heavy volumes of traffic may cause the problem to reoccur. Functional/Other ■ Roughness ■ Loss of skid Structural ■ Faulting Diamond grinding is not appropriate if significant faulting or other signs of structural failure (such as pumping or corner breaks) are present. Diamond grinding may not be appropriate if materials- related distresses are present. Soft aggregate will wear much quicker and require more frequent grinding. Site Restrictions Disposal of the ground slurry should be addressed during project development. Construction Considerations Typically constructed with a moving lane closure with traffic operating in the adjacent lanes. Often used in conjunction with other restoration techniques such as after the completion of load-transfer restoration. Expected Life May reduce faulting for 8 to 10 years and roughness for at least 5 years. Typical Costs Cost ranges from $1.50 to $6.50 per m2 ($1.25 to more than $7.00 per yd2) depending on the hardness of the aggregate. TABLE 12 Characteristics of diamond grinding EVALUATION FACTORS UNDERSEALING Climate Traffic Conditions Addressed Contraindications Description: Undersealing is the pressure insertion of a flowable material beneath a PCC slab to fill voids between the slab and base, thereby reducing deflections and, consequently, deflection-related distresses such as pumping or faulting. It is most often performed at areas where pumping and loss of support occur, such as beneath transverse joints and deteriorated cracks. The voids being filled by this technique are generally less than 3 mm (0.12 in.) thick. No studies are known to differentiate between the performance of undersealing in different environmental conditions. Performance is not known to be affected by different levels of ADT or percent trucks. Functional/Other Anticipates the development of roughness from faulting. Structural Fills voids that, if left unfilled, will lead to faulting and other structural deterioration. Performs best before faulting starts to develop. Significant faulting, or other signs of structural failure (such as pumping, mid-panel cracking, or corner breaks), suggest structural failure requiring more extensive rehabilitation. Additional strategies, such as dowel retrofitting, may be required for pavements without load transfer. Site Restrictions Voids must be identifiable and contained for undersealing to work. Construction Considerations Cement-fly ash grout is the most commonly used material, although asphalt has been used. Overfilling voids can contribute to worse problems than leaving them unfilled. Expected Life Performance has been extremely variable. Typical Costs Cost depends on the material used, the extent and size of the voids, and the size of the project. Cement-fly ash grout undersealing ranges from about $1.08 to $1.20 per m2 ($0.90 to $1.00 per yd2), while asphalt undersealing ranges from about $0.54 to $0.60 per m2 ($0.45 to $0.50 per yd2). TABLE 13 Characteristics of undersealing

16 EVALUATION FACTORS LOAD TRANSFER RESTORATION Climate Traffic Conditions Addressed Contraindications Description: Load transfer restoration (LTR) is the placement of load transfer devices across joints or cracks in an existing jointed PCC pavement to restore load transfer at these locations. Poor load transfer can lead to pumping, joint faulting, and corner breaks. LTR has been used in all climatic regions. The need for LTR increases with an increased ADT and percent trucks. Low- volume jointed concrete pavements that are not doweled may not need LTR. Functional/Other Can prevent the development of a rough ride caused by faulting. Structural Most effective on jointed concrete pavements that have poor load transfer at joints and/or transverse cracks but also have significant remaining structural life. The optimum time to apply this technique is when the pavement is just beginning to show signs of structural distress, such as pumping and the onset of faulting. Significant faulting, or other signs of structural failure (such as pumping, mid-panel cracking, or corner breaks). Pavements with little remaining life or materials-related distresses. Site Restrictions Can be performed with a single lane closure. Construction Considerations Agencies have experimented with different retrofit patterns. Two to four bars per wheelpath is typical. Care must be given to the selection of the patch material and isolation of the joint. Often performed in conjunction with diamond grinding. Expected Life A minimum expected life is 9 to 10 years (15). However, many load-transfer restoration projects have been in place around 20 years with little or no distress present (Puerto Rico) (16). Typical Costs For production jobs, the typical costs are $25 to $35 per dowel. Additional Information Repetitive applications will impart some structural benefit to the pavement in the form of additional load-carrying capability. TABLE 14 Characteristics of load transfer restoration EVALUATION FACTORS MAINTENANCE OF DRAINAGE FEATURES Climate Traffic Conditions Addressed Contraindications Description The following activities are used as needed to improve or enhance the drainage capabilities of the existing pavement: ■ Install/maintain reference markers at outlet locations. ■ Clear debris and vegetation at outlets and at culverts. ■ Inspect edge drain pipe using video equipment. ■ Flush/rod edge drain system with high pressure equipment. ■ Clean ditches and re-establish depths and grades. ■ Restore cross slopes through milling or surface leveling (HMA pavements only). ■ Regrade the shoulder to remove any buildup of dirt and debris. ■ Clean closed drainage systems, including drainage inlets, catch basins, and manholes. Maintenance of drainage features is not limited by climate or traffic conditions. Drainage maintenance does not address specific pavement condition. However, timely maintenance of drainage features helps to prevent the development of more serious deterioration. There are no contraindications for the maintenance of drainage features. Site Restrictions There are no site restrictions; this activity is performed entirely off the main roadway. Construction Considerations Drainage maintenance should be performed on a regular basis or whenever conditions warrant. Typical Costs Costs depend on activity and frequency. Additional Information The manner in which this activity is carried out varies widely among highway agencies. However, there is a far greater chance that the work will be completed if it is a programmed activity rather than one left for maintenance forces to do if all other activities have been completed. TABLE 15 Maintenance of drainage features

Maintenance of Drainage Features Maintenance of drainage features for both bituminous- surfaced and concrete-surfaced pavements are described in Table 15. Drainage impacts pavement performance in many ways. Poor surface drainage can lead to such undesirable con- ditions as splash and spray and or slippery pavements. Poor subsurface drainage can ultimately contribute to the reduced structural performance of the pavement. While the mainte- nance of features such as drainage outlets, headwalls, and edge drains may not be part of a pavement preventive maintenance program, the importance of performing routine maintenance of these features cannot be overemphasized. Drainage features are incorporated in a pavement structure to prevent the devel- opment and acceleration of moisture-related deterioration; 17 failure to maintain these features in operable condition can contribute to the loss of pavement serviceability. SUMMARY The literature search performed for this project shows that there is little work being done on the timing of preventive maintenance treatments. However, there is a general consen- sus on the concepts and definition of preventive mainte- nance, and on the treatments used in preventive maintenance programs. Important attributes of preventive maintenance treatments may be considered for selecting treatments to be included in a preventive maintenance program and for deter- mining when such treatments should be applied.

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Optimal Timing of Pavement Preventive Maintenance Treatment Applications Get This Book
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TRB's National Cooperative Highway Research Program (NCHRP) Report 523: Optimal Timing of Pavement Preventive Maintenance Treatment Applications describes a methodology for determining the optimal timing for the application of preventive maintenance treatments to flexible and rigid pavements. NCHRP Report 523 also presents the methodology in the form of a macro-driven Microsoft Excel Visual Basic Application--designated OPTime.

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